Extremity imaging apparatus for cone beam computed tomography

ABSTRACT

A cone beam computed tomography imaging system uses a C-shaped structure to revolve a source and detector around an imaging axis. To balance the system a counterweight is attached to the C-shaped structure at one end adjacent to the detector. The source is attached to another end of the C-shaped structure opposite the detector.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and is a U.S. National Phase filing of PCT Application PCT/US2014/047518 filed Jul. 22, 2014, entitled “EXTREMITY IMAGING APPARATUS FOR CONE BEAM COMPUTED TOMOGRAPHY”, in the name of Anthony Dirisio, which is incorporated herein in its entirety.

FIELD OF THE INVENTION

The invention relates generally to diagnostic imaging and in particular to cone beam imaging systems used for obtaining volume images of extremities.

BACKGROUND OF THE INVENTION

3-D volume imaging has proved to be a valuable diagnostic tool that offers significant advantages over earlier 2-D radiographic imaging techniques for evaluating the condition of internal structures and organs. 3-D imaging of a patient or other subject has been made possible by a number of advancements, including the development of high-speed imaging detectors, such as digital radiography (DR) detectors that enable multiple images to be taken in rapid succession.

Cone beam computed tomography (CBCT) or cone beam CT technology offers considerable promise as one type of diagnostic tool for providing 3-D volume images. Cone beam CT systems capture volumetric data sets by using a high frame rate digital radiography (DR) detector and an x-ray source, typically affixed to a gantry that rotates about the object to be imaged, directing, from various points along its orbit around the subject, a divergent cone beam of x-rays toward the subject. The CBCT system captures projections throughout the rotation, for example, one 2-D projection image at every degree of rotation. The projections are then reconstructed into a 3D volume image using various techniques. Among well known methods for reconstructing the 3-D volume image from the 2-D image data are filtered back projection approaches.

Although 3-D images of diagnostic quality can be generated using CBCT systems and technology, a number of technical challenges remain. In some cases, for example, there can be a limited range of angular rotation of the x-ray source and detector with respect to the subject. CBCT imaging of legs, arms, and other extremities can be hampered by physical obstruction from a paired extremity. This is an obstacle that is encountered in obtaining CBCT image projections for the human leg or knee, for example. Not all imaging positions around the knee are accessible; the patient's own anatomy often prevents the radiation source and image detector from being positioned over a portion of the scan circumference.

To illustrate the problem faced in CBCT imaging of the knee, the top view of FIG. 1 shows the circular scan paths for a radiation source 22 and detector 24 when imaging the right knee R of a patient as a subject 20. Various positions of radiation source 22 and detector 24 are shown in dashed line form. Source 22, placed at some distance from the knee, can be positioned at different points over an arc of about 200 degrees; with any larger arc the paired extremity, left knee L, blocks the way. Detector 24, smaller than source 22 and typically placed very near subject 20, can be positioned between the patient's right and left knees and is thus capable of positioning over the full circular orbit.

A full 360 degree orbit of the source and detector is not needed for conventional CBCT imaging; instead, sufficient information for image reconstruction can be obtained with an orbital scan range that just exceeds 180 degrees by the angle of the cone beam itself, for example. However, in some cases it can be difficult to obtain much more than about 180 degree revolution for imaging the knee or other joints and other applications. Moreover, there can be diagnostic situations in which obtaining projection images over a certain range of angles has advantages, but patient anatomy blocks the source, detector, or both from imaging over that range.

Still other difficulties with conventional solutions for extremity imaging relate to poor image quality. For image quality, the CBCT sequence requires that the detector be positioned close to the subject and that the source of the cone beam radiation be at a sufficient distance from the subject. This provides the best image and reduces image truncation and consequent lost data.

CBCT imaging represents a number of challenges that also affect other types of volume imaging that employ a radiation source and detector orbiting an extremity over a range of angles. There are various tomographic imaging modes that can be used to obtain depth information for a scanned extremity.

In summary, for extremity imaging, particularly for imaging the lower paired extremities, a number of improvements are needed, including the following:

-   -   (i) improved placement of the radiation source and detector         relative to the imaged subject to provide acceptable radiation         levels and image quality (e.g., reduced relative movement         between a source and a detector) throughout the scanning         sequence, with the capability for at least coarse automated         setup for examining an extremity under favorable conditions; or     -   (ii) improved patient accessibility, so that the patient does         not need to contort, twist, or unduly stress limbs or joints         that may have been injured in order to provide images of those         body parts.

In summary, the capability for straightforward configuration and positioning of the imaging apparatus allows the advantages of CBCT imaging to be adaptable for use with a range of extremities, to obtain volume images under a suitable imaging modality, with the image extremity presented at a suitable orientation under both load-bearing and non-load-bearing conditions, and with the patient appropriately standing or seated.

SUMMARY OF THE INVENTION

An aspect of this application is to advance the art of medical digital radiography.

Another aspect of this application is to address, in whole or in part, at least the foregoing and other deficiencies in the related art.

It is another aspect of this application to provide, in whole or in part, at least the advantages described herein.

It is another aspect of this application to advance the art of diagnostic imaging of extremity body parts, particularly jointed or load-bearing, paired extremities such as knees, legs, ankles, fingers, hands, wrists, elbows, arms, and shoulders.

It is another aspect of this application to provide apparatus and/or method embodiments that adapt to imaging conditions suitable for a range of extremities and/or allows the patient to be in a number of positions for suitable imaging of the extremity.

It is another aspect of this application to provide radiographic imaging apparatus and/or method embodiments that can separately provide a detector and a counterweight to a scan gantry mechanism.

It is another aspect of this application to provide radiographic imaging apparatus and/or method embodiments that can provide a detector and counterweight configured to move independently from one another.

It is another aspect of this application to provide radiographic imaging apparatus and/or method embodiments that can provide two separate supports individually for a detector and a counterweight that can allow different materials or characteristics for the separate supports or that can reduce the total weight of materials from that used to position and support the detector and counterweight as a single unit.

It is another aspect of this application to provide radiographic imaging apparatus and/or method embodiments that can provide the ability to position the detector relative to the source during scanning with reduced movement or vibration.

It is another aspect of this application to provide radiographic imaging apparatus and/or method embodiments that can provide a prescribed size clearance gap between a detector and a counterweight.

It is another aspect of this application to provide radiographic imaging apparatus and/or method embodiments that can provide separate supports individually for a detector and a counterweight to increase a scan volume of a volumetric radiographic imaging system

These objects are given only by way of illustrative example, and such objects may be exemplary of one or more embodiments of the invention. Other desirable objectives and advantages inherently achieved by the disclosed invention may occur or become apparent to those skilled in the art. The invention is defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of the embodiments of the invention, as illustrated in the accompanying drawings. The elements of the drawings are not necessarily to scale relative to each other.

FIG. 1 is a schematic view showing the geometry and limitations of CBCT scanning for portions of the lower leg.

FIG. 2 shows a top and perspective view of the scanning pattern for an imaging apparatus according to an embodiment of the application.

FIG. 3A is a perspective view showing patient access to an imaging apparatus according to an embodiment of the application.

FIG. 3B is a top view showing a sequence of steps for enclosing the extremity to be imaged within the path of the detector transport.

FIG. 3C is a perspective view showing patient access to another imaging apparatus according to an embodiment of the application.

FIG. 3D is a perspective view showing a revolvable gantry for another imaging apparatus according to an embodiment of the application.

FIG. 4 show portions of the operational sequence for obtaining CBCT projections of a portion of a patient's leg at a number of angular positions when using the imaging apparatus according to an embodiment of the application.

FIG. 5 is a perspective view that shows a CBCT imaging apparatus for extremity imaging according to an embodiment of the application.

FIG. 6A shows internal components used for imaging ring translation and positioning.

FIG. 6B shows reference axes for rotation and translation.

FIG. 6C is a schematic diagram that shows components of the positioning system for the imaging scanner.

FIG. 6D is a perspective view showing some of the components of a vertical translation apparatus.

FIG. 6E shows the CBCT imaging apparatus with covers installed.

FIG. 7A shows translation of the imaging ring with respect to a vertical or z-axis.

FIG. 7B shows rotation of the imaging ring about an α-axis that is orthogonal to the z-axis.

FIG. 7C shows rotation of the imaging ring about a γ-axis that is orthogonal to the α-axis.

FIG. 7D shows the position of operator controls for fine-tune position of the imaging scanner.

FIG. 7E shows an enlarged view of the positioning controls.

FIG. 8 is a perspective view that shows the extremity imaging apparatus configured for knee imaging with a standing patient.

FIG. 9 is a perspective view that shows the extremity imaging apparatus configured for foot or ankle imaging with a standing patient.

FIG. 10 is a perspective view that shows the extremity imaging apparatus configured for knee imaging with a seated patient.

FIG. 11 is a perspective view that shows the extremity imaging apparatus configured for elbow imaging with a seated patient.

FIG. 12A is a top view of the scanner components of an extremity imaging apparatus according to an embodiment of the application.

FIG. 12B is a perspective view of a frame that supports scanner components of an extremity imaging apparatus according to an embodiment of the application.

FIG. 12C is a perspective view of a frame that supports scanner components of an extremity imaging apparatus with added counterweight according to an embodiment of the application.

FIG. 13A is a top view of the imaging scanner showing the door open position.

FIG. 13B is a perspective view of the imaging scanner showing a door closing position.

FIG. 13C is a top view of the imaging scanner showing the door closed position.

FIG. 13D is a perspective view showing the door in closed position.

FIG. 14A is a top view of the imaging scanner with a number of its internal imaging components shown, at one extreme end of the imaging scan.

FIG. 14B is a top view of the imaging scanner with a number of its internal imaging components shown, at the opposite extreme end of the imaging scan from that shown in FIG. 14A.

FIG. 14C is a top view of the imaging scanner with its housing shown.

FIG. 14D is a top view of the imaging scanner with internal imaging components and central arc angles shown.

FIG. 15 is a top view that shows movement of scanning components that is allowable when the door of the scanner is closed.

FIG. 16 is a perspective view of the scanner with the housing covers removed, showing the door in closed position.

FIGS. 17A and 17B are diagrams that show additional features of exemplary gantry and/or transport mechanism for use in CBCT X-ray imaging systems.

FIGS. 18A-18D are diagrams that show an exemplary embodiment of a counterweight support mechanism for use with a gantry for a transport mechanism for use in CBCT X-ray imaging systems according to the application.

FIGS. 19A-19B are diagrams that show an exemplary embodiment of a counterweight support mechanism for use with a gantry for a transport mechanism for use in CBCT radiographic imaging systems or the like according to the application.

FIGS. 20A-20B are diagrams that show an exemplary embodiment of a counterweight support mechanism for use with a gantry for a transport mechanism for use in CBCT radiographic imaging systems or the like according to the application.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following is a description of exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

For illustrative purposes, principles of the invention are described herein by referring mainly to exemplary embodiments thereof. However, one of ordinary skill in the art would readily recognize that the same principles are equally applicable to, and can be implemented in, all types of radiographic imaging arrays, various types of radiographic imaging apparatus and/or methods for using the same and that any such variations do not depart from the true spirit and scope of the application. Moreover, in the following description, references are made to the accompanying figures, which illustrate specific exemplary embodiments. Electrical, mechanical, logical and structural changes can be made to the embodiments without departing from the spirit and scope of the invention.

In the context of the application, the term “extremity” has its meaning as conventionally understood in diagnostic imaging parlance, referring to knees, legs, ankles, fingers, hands, wrists, elbows, arms, and shoulders and any other anatomical extremity. The term “subject” is used to describe the extremity of the patient that is imaged, such as the “subject leg”, for example. The term “paired extremity” is used in general to refer to any anatomical extremity wherein normally two or more are present on the same patient. In the context of the application, the paired extremity is not imaged unless necessary; only the subject extremity is imaged. In one embodiment, a paired extremity is not imaged to reduce patient dose.

A number of the examples given herein for extemporary embodiments of the application focus on imaging of the load-bearing lower extremities of the human anatomy, such as the leg, the knee, the ankle, and the foot, for example. However, these examples are considered to be illustrative and non-limiting.

In the context of the application, the term “arc” or, alternately, or arcuate has a meaning of a portion of a curve, spline or non-linear path, for example as being a portion of a curve of less than or greater than 360 degrees.

The term “actuable” has its conventional meaning, relating to a device or component that is capable of effecting an action in response to a stimulus, such as in response to an electrical signal, for example.

As used herein, the term “energizable” relates to a device or set of components that perform an indicated function upon receiving power and, optionally, upon receiving an enabling signal.

In the context of the application, two elements are considered to be substantially orthogonal if their angular orientations differ from each other by 90 degrees, +/− no more than about 10 degrees. It is instructive to observe that the mathematical definition of a cylinder includes not only the familiar “can-shaped” right circular cylinder, but also any number of other shapes. The outer surface of a cylinder is generated by moving a first straight line element along a closed curve or other path along a base plane, while maintaining the first straight line element parallel to a second, fixed straight line that extends out from the base plane, wherein the moving first straight line intersects a fixed closed curve or base in the base plane. A cube, for example, is considered to have a cylindrical shape according to this definition. A can-shaped cylinder of revolution, for example, is generated when the moving first straight line intersects a circle in the base plane at a right angle. An object is considered to be substantially cylindrical when its overall surface shape is approximated by a cylinder shape according to this definition, with allowance for standard edge rounding, protruding or recessed mechanical and electrical fasteners, and external mounting features.

Certain exemplary embodiments according to the application address the difficulties of extremity imaging by providing an imaging apparatus that defines coordinated non-linear source and detector paths (e.g., orbital, curved, or concentric about a center point), wherein components that provide the source and detector paths are configured to allow patient access prior to and following imaging and configured to allow the patient to sit or stand with normal posture during the CBCT image capture series. Certain exemplary embodiments provide this capability by using a detector transport device that has a circumferential access opening allowing positioning of the extremity, wherein the detector transport device is revolved about the positioned extremity once it is in place, enclosing (e.g., partially, substantially, fully) the extremity as it is revolved through at least a portion of the scan.

It is instructive to consider dimensional attributes of the human frame that can be considerations for design of CBCT equipment for scanning extremities. For example, an adult human patient of average height in a comfortable standing position has left and right knees generally anywhere from about 10 to about 35 cm apart. For an adult of average height, exceeding about 35-40 cm (14-15.7 inches) between the knees becomes increasing less comfortable and out of the range of normal standing posture. It is instructive to note that this constraint makes it impractical to use conventional gantry solutions for obtaining the needed 2-D image sequence. For certain exemplary embodiments, either the source or the detector must be able to pass between the legs of a standing patient for knee CBCT imaging, a capability not available with gantry or other conventional solutions.

The perspective and corresponding top views of FIG. 2 show how the scanning pattern is provided for components of CBCT imaging apparatus 10 according to an embodiment of the application. A detector path 28 of a suitable radius R1 from a central axis β is provided for a detector device by a detector transport 34. A source path 26 of a second, larger radius R2 is provided for a radiation source by a source transport 32. In one embodiment, a non-linear source path 26 is greater in length than a non-linear detector path 24. According to an embodiment of the application, described in more detail subsequently, the same transport system provides both detector transport 34 and source transport 32. The extremity, subject 20, is preferably substantially centered along central axis β so that central axis β can be considered as a line through points in subject 20. In one embodiment, an imaging bore or the CBCT apparatus can include or encompass the central axis β. The limiting geometry for image capture is due to the path of source transport 32, blocked by gap 38 (e.g., for patient anatomy, such as by a paired limb), and thus limited typically to less than about 220 degrees, as noted previously. The circumferential gap or opening 38 can occupy the space between the endpoints of the arc of source path 26. Gap or opening 38 gives space for the patient a place to stand, for example, while one leg is being imaged.

Detector path 28 can extend through circumferential gap 38 to allow scanning, since the detector is not necessarily blocked by patient anatomy but can have a travel path at least partially around an imaged extremity that can extend between the standing patient's legs. Embodiments of the present invention allow temporary restriction of the detector path 28 to allow access for the patient as part of initial patient positioning. The perspective view in FIG. 2, for example, shows detector transport 34 rotated to open up circumferential gap 38 so that it extends from the axis β (e.g., beyond a source path or housing). With detector transport 34 translated to the open position shown in FIG. 3A, the patient can freely move in and out of position for imaging. When the patient is properly in position, detector transport 34 is revolved about axis βby more than 180 degrees; according to an embodiment of the application, detector transport 34 is revolved about axis β by substantially 200 degrees. This patient access and subsequent adjustment of detector transport 34 is shown in successive stages in FIG. 3B. This orbital movement confines the extremity to be imaged more effectively and places detector 24, not visible in FIGS. 2-3C due to the detector transport 34 housing, in position near subject 20 for obtaining the first projection image in sequence. In one embodiment, a detector transport 34 can include shielding or a door over part of the detector path, and/or the gap 38. As shown in FIG. 3D, a revolvable gantry 68 allows detector 24 and source 22 to revolve around imaging volume of another imaging apparatus 10′ according to an embodiment of the application.

Circumferential gap or opening 38 not only allows access for positioning of the subject leg or other extremity, but also allows sufficient space for the patient to stand in normal posture during imaging, placing the subject leg for imaging in the central position along axis β (FIG. 2) and the non-imaged paired leg within the space defined by circumferential gap 38. Circumferential gap or opening 38 extends approximately 180 degrees minus the fan angle (e.g., between ends of the source path), which is determined by source-detector geometry and distance. Circumferential gap or opening 38 permits access of the extremity so that it can be centered in position along central axis β. Once the patient's leg or other extremity is in place, detector transport 34, or a hooded cover or hollow door or other member that defines this transport path, can be revolved into position, closing the detector portion of circumferential gap or opening 38.

By way of example, the top views of FIG. 4 show portions of the operational sequence for obtaining CBCT projections of a portion of a patient's leg at a number of angular positions when using a CBCT imaging apparatus. The relative positions of radiation source 22 and detector 24, which may be concealed under a hood or chassis, as noted earlier, are shown in FIG. 4. The source 22 and detector 24 can be aligned so the radiation source 22 can direct radiation toward the detector 24 (e.g., diametrically opposite) at each position during the CBCT scan and projection imaging. The sequence begins at a begin scan position 50, with radiation source 22 and detector 24 at initial positions to obtain an image at a first angle. Then, both radiation source 22 and detector 24 revolve about axis β (e.g., imaging volume) as represented in interim scan positions 52, 54, 56, and 58. Imaging terminates at an end scan position 60. As this sequence shows, source 22 and detector 24 are in opposing positions relative to subject 20 at each imaging angle. Throughout the scanning cycle, detector 24 is within a short distance D1 of subject 20. Source 22 is positioned beyond a longer distance D2 of subject 20. The positioning of source 22 and detector 24 components on each path can be carried out by separate actuators, one for each transport path, or by a single rotatable member, as described in more detail subsequently. It should be noted that scanning motion in the opposite direction, that is, clockwise with respect to the example shown in FIG. 4, is also possible, with the corresponding changes in initial and terminal scan positions.

Given this basic operation sequence in which the source 22 and detector 24 orbit the extremity, the usefulness of an imaging system that is adaptable for imaging patient extremities with the patient sitting or standing and in load-bearing or non load-bearing postures can be appreciated. The perspective view of FIG. 5 shows a CBCT imaging apparatus 100 for extremity imaging according to an embodiment of the application. Imaging apparatus 100 has a gimballed imaging ring or scanner 110 that houses and conceals source 22 and detector 24 within a housing 78. FIG. 5 shows their supporting transport mechanisms. Scanner 110 is adjustable in height and rotatable in gimbaled fashion about non-parallel axes, such as about substantially orthogonal axes as described in subsequent figures, to adapt to various patient postures and extremity imaging conditions. A support column 120 supports scanner 110 on a yoke, or bifurcated or forked support arm 130, a rigid supporting element that has adjustable height and further provides rotation of scanner 110 as described subsequently. Support column 120 can be fixed in position, such as mounted to a floor, wall, or ceiling. According to portable CBCT embodiments such as shown in FIG. 6A and elsewhere, support column 120 mounts to a support base 121 that also includes optional wheels or casters 122 for transporting and maneuvering imaging apparatus 100 into position. A control panel 124 can provide an operator interface, such as a display monitor, for entering instructions for apparatus 100 adjustment and operation. In one embodiment, the control panel 124 can include a processor or computer (e.g., hardware, firmware and/or software) to control operations of the CBCT system 100. Support column 120 can be of fixed height or may have telescoping operation, such as for improved visibility when apparatus 100 is moved.

Vertical and Rotational Movement

FIG. 6A shows portions of exemplary internal imaging and positioning mechanisms (with covers removed) for scanner 110 that allow imaging apparatus 100 the capability for imaging extremities with a variety of configurations. FIG. 6B shows rotation axes definitions for scanner 110 positioning. The α-axis and the γ-axis are non-parallel, to allow gimbaled action. According to an embodiment of the application as shown in FIG. 6A, the α-axis and the γ-axis are mutually orthogonal. The α-axis is substantially orthogonal to the z-axis. The intersection of the α-axis and the γ-axis can be offset from support column 120 by some non-zero distance.

First considering the z-axis, FIG. 6A shows an exemplary embodiment to achieve vertical motion. Within support column 120, a vertical carriage translation element 128 is actuated in order to travel upwards or downwards along column 120 within a track 112 in a vertical direction. Carriage translation element 128 has a support shaft 132 that is coupled to an actuator 136 for providing α-axis rotation to forked or C-shaped support arm 130. Forked support arm 130, shown only partially in FIG. 6A to allow a better view of underlying components, is coupled to support shaft 132. X-ray source 22 and receiver 24 are mounted on a rotatable gantry 36 for rotation about a scan or central axis, designated as the β axis. Axis β is orthogonal to the α-axis and the γ-axis.

It can be appreciated that z-axis translation can be effected in a number of ways. Challenges that must be addressed by the type of system that is used include handling the weight of forked support arm 130 and the imaging scanner 110 that arm 130 supports. This can easily weigh a few hundred pounds. In addition, precautions must be provided for handling conditions such as power loss, contact with the patient, or mechanical problems that hamper positioning movement or operation. According to an embodiment of the application, as shown schematically in FIG. 6C and in the perspective view of FIG. 6D, a vertical actuator 129 rotates a threaded shaft 123. Vertical carriage translation element 128 employs a ball screw mount apparatus 125 to translate rotational motion to the needed linear (e.g., z-direction) motion, thus urging vertical carriage translation element 128 upward or allowing vertical carriage translation element 128 to move downward. Ball screw translation devices are advantaged for handling high weight loads and are typically more efficient than other types of translators using threaded devices. The use of a ball screw arrangement also allows a small motor to drive the shaft that lifts scanner 110 into position and can help to eliminate the need for a complex and bulky counterweight system for allowing control of vertical movement. An encoder 145, such as a linear encoder element, can provide feedback signals that are used to indicate the vertical position of vertical carriage translation element 128.

Vertical carriage translation element 128 travels inside track 112 formed in support column 120 (FIG. 6A); wheels 138 help to guide translation element 128 within the slots. Paired wheels 138 can be orthogonal to each other to provide centering within column 120.

A braking system can also be provided for support column 120. Spring-loaded brakes 142 (FIG. 6D) are positioned to actuate and grip shaft 123 or other mechanical support when mechanical difficulties, power failure, or other conditions are detected. A sensor 144, such as a load cell, is configured to sense rapid movement or interference conditions that are undesirable and to cause brakes 142 actuation.

Other features of support column 120 for vertical translation include built-in redundancy, with springs to absorb weight and impact, the load cell to sense a mechanical problem including obstruction by the patient, and manually operable brake mechanisms.

It should be noted that other types of translation apparatus could be used for providing vertical movement of vertical carriage translation element 128. In one embodiment, the β-axis can be implemented +/− up to 10 degrees. In one embodiment, the horizontal α-axis can be implemented +/− up to 10 degrees. In one embodiment, the γ-axis for a CBCT apparatus can be +/− up to 45 degrees.

Gimbaled Arrangement for Scanner

Forked support arm 130 can support scanner 110 in a gimbaled arrangement. Source 22 and detector 24 are shown on gantry 36 for reference in FIG. 6A and covered in the alternate view of FIG. 6E. Vertical carriage translation element 128 is configured to ride within a track 112 (FIG. 6A) within support column 120. For certain exemplary embodiments, some level of manual operability can be provided, such as for power loss situations.

According to an alternate embodiment of the application, vertical carriage translation element 128 can be a motor that moves vertically along supporting threaded shaft 132; alternately, vertical carriage translation element 128 can be driven using a chain, pulley, or other intermediate mechanism that has considerable counterweights for manually raising and lowering vertical carriage translation element 128 and its connected forked support arm 130 and components within support column 120.

Next, considering the α-axis movement of forked support arm 130, in one embodiment a rotational actuator 136 can be energizable to allow rotation of shaft 132 (FIG. 6A). This rotational actuation can be concurrent with z-axis translation as well as with rotation with respect to the γ-axis.

Forked support arm 130 allows movement relative to the γ-axis according to the position and angle of forked support arm 130. In the example of FIG. 6A, the γ-axis is oriented vertically, substantially in parallel with the z-axis. FIG. 6E shows the γ-axis oriented horizontally. A pivoting mount 140 with a rotational actuator 146, provided by forked support arm 130, allows rotation along the γ-axis. The gimbaled combination of α-axis and γ-axis rotation can allow the imaging apparatus to be set up for imaging in a number of possible positions, with the patient standing, seated, or prone.

An exemplary positioning capability of the imaging apparatus 100 is shown in FIGS. 7A-7C. FIG. 7A shows movement of forked support arm 130 on support column 120 to provide z-axis (vertical) translation of scanner 110. FIG. 7B shows rotation of forked support arm 130 about the horizontal α-axis. FIG. 7C shows rotation about the γ-axis as defined by the C-arm arrangement of forked support arm 130.

Sequence and Controls for Positioning Support Arm 130

According to an exemplary embodiment, an initial set of operator commands automatically configure CBCT imaging apparatus 100 to one of a well-defined set of default positions for imaging, such as those described subsequently. The patient waits until this initial setup is completed. Then, the patient is positioned at CBCT imaging apparatus 100 and any needed adjustments in height (z-axis) or rotation about the α or γ axes can be made by the technician. This type of fine-tuning adjustment is at slow speeds for increased patient comfort and because only incremental changes to position are needed in most cases.

FIG. 7D and the enlarged view of FIG. 7E show user control stations 156, 158 that are provided on arm 130 (with scanner 110 removed for improved visibility) for operator adjustment of z-axis translation and α-and γ-axis rotation as described in FIGS. 7A-7C. Both control stations 156 and 158 are essentially the same, duplicated to allow easier access for the operator for different extremity imaging arrangements. By way of example, FIG. 7E shows an enlarged view of control station 158. An enablement switch 159 is pressed to activate a control 160 and an associated indicator illuminates when control 160 is active or enabled. As a patient safety feature to protect from inadvertent patient contact with the controls in some imaging configurations, one or both control stations 156, 158 are disabled. One or both control stations 156, 158 can also be disabled following a time-out period after switch 159 has been pressed. An emergency stop control 162 can stop all motion of the imaging apparatus including downward motion of support arm 130.

Still referring to FIG. 7E, control 160 can activate any of the appropriate actuators for z-axis translation, α-axis rotation and/or γ-axis rotation. Exemplary responses of the system can be based on operator action, as follows:

-   -   (i) z-axis vertical movement is effected by pressing control 160         in a vertical upward or downward direction. The control logic         adjusts for the angular position of the support arm 130, so that         pressing the control upward provides z-axis movement regardless         of support arm 130 orientation.     -   (ii) α-axis rotation is effected by rotating control 160.         Circular motion of control 60 in an either clockwise (CW) or         counterclockwise (CCW) direction causes corresponding rotation         about the α axis.     -   (iii) γ-axis rotation is effected by horizontal left-to-right or         right-to-left movement of control 60. As with z-axis movement,         control logic adjusts for the angular position of the support         arm 130, so that left-right or right-left movement is relative         to the operator regardless of support arm 130 orientation.

It should be noted that CBCT imaging apparatus 100 as shown in FIG. 6E provides at least three degrees of freedom (DOF) for scanner 110 positioning. In addition to the z-axis translation and rotation about α- and γ-axes previously described, casters 122 allow rotation of scanner 110 position with respect to the z-axis as well as translation along the floor.

Configurations for Imaging Various Extremities

Given the basic structure described with reference to FIGS. 6A-7D, the positioning versatility of scanner 110 for various purposes can be appreciated. Subsequent FIGS. 8-11 show, by way of example, how this arrangement serves different configurations for extremity imaging.

FIG. 8 shows an exemplary scanner 110 positioning for a knee exam, where subject 20 is a standing patient. An optional patient support bar 150 can be attached to support column 120. In one embodiment, support bar 150 is mounted to vertical carriage translation element 128. Accordingly, as the vertical carriage translation element 128 moves, a corresponding position of the support bar 150 can be moved. According to an alternate embodiment of the application, the support bar 150 can be mounted to the scanner 110, such as to the cover of scanner 110 or to the forked support arm 130. In contrast, embodiments of support bar 150 can be motionless during imaging or during a scan by the scanner 110. For this embodiment, vertical adjustment along the z-axis sets the knee of the patient at the center of the scanner 110. Forked support arm 130 is arranged so that the plane that contains both the α-axis and the γ-axis is substantially horizontal. Patient access is through an opening, circumferential gap or opening 38 in scanner 110. A door 160 is pivoted into place across gap 38 to enclose an inner portion of circumferential gap or opening 38. Door 160 fits between the legs of the patient once the knee of the patient is positioned.

Certain exemplary embodiments of optional patient support bar 150 can be mounted to movable portions of the CBCT apparatus 100, preferably to have a prescribed spatial relationship to an imaging volume. For such embodiments, a presence detector 151 can be configured to detect when the support bar 150 is mounted to the CBCT system 100. When detected, a controller or the like, for example, in the control panel 124, can calculate scanner 110, and/or forked support arm 130 movements to prevent collisions therebetween with the affixed support bar 150. Thus when attached, support bar 150 can limit motion of the scanner 110. Exemplary presence detectors 151 can include but are not limited to magnetic detectors, optical detectors, electro-mechanical detectors or the like. As shown in FIG. 9, a pair of optional or removable support arms 150 can be affixed to the vertical carriage translation element 128 and have their attachment reported by a pair of presence detectors 151.

For FIG. 8 and selected subsequent exemplary embodiments, door 160, once pivoted into its closed position, can effectively extend the imaging path by protecting and/or providing the curved detector transport 34 path as shown in FIG. 4. With this arrangement, when door 160 is closed to protect the transport path, the knee can be examined under weight-bearing or non-weight-bearing conditions. By enclosing the portion of detector transport 34 path that crosses opening 38, door 160 enables the extremity to be positioned suitably for 3D imaging and to be maintained in position between the source and detector as these imaging components orbit the extremity in the CBCT image capture sequence.

FIG. 9 shows scanner 110 positioning for a foot or ankle exam wherein subject 20 is a standing patient. With this configuration, scanner 110 is lowered to more effectively scan the area of interest. The plane that contains both the α-axis and the γ-axis is approximately 10 degrees offset from horizontal, rotated about the γ axis. A step 116 is provided across circumferential gap or opening 38 for patient access.

FIG. 10 shows scanner 110 positioning for a knee exam with the patient seated. For this configuration, forked support arm 130 is elevated with respect to the z-axis. Rotation about the α-axis orients the γ-axis so that it is vertical or nearly vertical. Circumferential gap or opening 38 is positioned to allow easy patient access for imaging the right knee. It should be noted that 180 degree rotation about the γ-axis would position circumferential gap or opening 38 on the other side of scanner 110 and allow imaging of the other (left) knee.

Alternative scanner 110 positioning can include foot or ankle exam with the patient seated, toe exam with the patient seated, a hand exam, with the patient seated.

FIG. 11 shows scanner 110 positioning for an elbow exam, with the patient seated. For this configuration, forked support arm 130 is again elevated with respect to the z-axis. Rotation about the γ-axis positions circumferential gap 38 suitably for patient access. Further rotation about the α-axis may be provided for patient comfort.

In one embodiment of CBCT imaging apparatus 100, the operator can first enter an instruction at the control console or control panel 124 that specifies the exam type (e.g., for the configurations shown in FIGS. 8-11). The system then automatically adapts the chosen configuration, prior to positioning the patient. Once the patient is in place, manually controlled adjustments to z-axis and α- and γ-axes rotations can be made, as described previously.

Scanner Configuration and Operation

As previously described with reference to FIGS. 1-4, scanner 110 is configured to provide suitable travel paths for radiation source 22 and detector 24 about the extremity that is to be imaged, such as those shown in FIGS. 8-11. Scanner 110 operations in such various exemplary configurations can present a number of requirements that can be at least somewhat in conflict, including the following:

-   -   (i) Imaging over a large range of angles, preferably over an arc         exceeding 180 degrees plus the fan angle of the radiation         source.     -   (ii) Ease of patient access and extremity positioning for a wide         range of limbs.     -   (iii) Capability to allow both weight-bearing and         non-weight-bearing postures that allow imaging with minimized         strain on the patient.     -   (iii) Enclosure to prevent inadvertent patient contact with         moving parts.     -   (iv) Fixed registration of source to detector throughout the         scan cycle.

The top view of FIG. 12A shows a configuration of components of scanner 110 that orbit subject 20 according to an exemplary embodiment of the application. One or more sources 22 and detector 24 are mounted in a cantilevered C-shaped gantry 36 that is part of a transport assembly 170 that can be controllably revolved (e.g., rotatable over an arc about central axis β). Source 22 and detector 24 are thus fixed relative to each other throughout their movement cycle. An actuator 172 is mounted to a frame 174 of assembly 170 and provides a moving hinge for gantry pivoting. Actuator 172 is energizable to move gantry 36 and frame 174 with clockwise (CW) or counterclockwise (CCW) rotation as needed for the scan sequence. Cover 184 can reduce or keeps out dust and debris and/or better protect the operator and patient from contact with moving parts.

The perspective view of FIG. 12B shows frame 174 and gantry 36 of transport assembly 170 in added detail. Actuator 172 cooperates with a belt 178 to pivot frame 174 for moving source 22 and detector 24 about axis β. The perspective view of FIG. 12C shows frame 174 with added counterweights 182 for improved balance of the cantilevered arrangement.

Because a portion of the scan arc that is detector path 28 (FIG. 2) passes through the circumferential gap or opening 38 that allows patient access, this portion of the scan path should be isolated from the patient. FIGS. 13A, 13B, and 13C show, in successive positions for closing over gap or opening 38, a slidable door 176 that is stored in a retracted position within a housing 180 for providing a covering over the detector path 28 once the patient is in proper position. In one embodiment, door 176 can be substantially a hollow structure that, when closed, allows passage of the detector 24 around the patient's extremity. Referring to FIG. 12B, the portion of frame 174 of gantry 36 that supports detector 24 can pass through the hollow inner chamber provided by door 176 during the imaging scan. At the conclusion of the imaging sequence, frame 174 of gantry 36 rotates back into its home position and door 176 is retracted to its original position for patient access or egress within housing 180. In one embodiment, the door 176 is manually opened and closed by the operator. In one embodiment, interlocks are provided so that movement of scanning transport components (rotation of cantilevered frame 174) is only possible while full closure of the door 176 is sensed.

FIG. 13B also shows top and bottom surfaces 190 and 192, respectively, of housing 180. An outer circumferential surface 194 extends between and connects top and bottom surfaces 190 and 192. An inner circumferential surface 196 is configured to connect the top and bottom surfaces 190 and 192 to form a central opening 198 extending from the first surface to the second surface, where the central opening 198 surrounds the βaxis.

As shown with respect to FIGS. 2 and 4, in one embodiment radiation source 22 and detector 24 each can orbit the subject along an arc with radii R2 and R1, respectively. According to an alternate embodiment, within source transport 32, a source actuator could be used, cooperating with a separate, complementary detector actuator that is part of detector transport 34. Thus, two independent actuator devices, one in each transport assembly, can be separately controlled and coordinated by an external logic controller to move source 22 and detector 24 along their respective arcs, in unison, about subject 20.

In the context of the present disclosure, a surface is considered to be “substantially” flat if it has a radius of curvature that exceeds about 10 feet.

The perspective view of FIG. 10 shows the extremity CBCT imaging apparatus 100 configured for knee imaging with a seated patient. From FIG. 10, it can be seen that the patient needs room outside of the scan volume for comfortable placement of the leg that is not being imaged. For this purpose, housing 78 is shaped to provide additional clearance.

As is readily visible from FIGS. 8-11 and 13A-13D, imaging scanner 110 has a housing 78. According to one embodiment of the application, housing 78 is substantially cylindrical; however, a cylindrical surface shape for housing 78 is not required. By substantially cylindrical is meant that, to at least a first approximation, the housing 78 surface shape closely approximates a cylinder, with some divergence from strict geometric definition of a cylinder and with a peripherally gap and some additional features for attachment and component interface that are not in themselves cylindrical.

FIGS. 14A-14D show a number of features that are of interest for an understanding of how scanner 110 is configured and operated (e.g., scans). FIG. 14A shows how peripheral gap 38 is formed by housing 78, according to an embodiment of the application. Scan volume 228, outlined with a dashed line, is defined by the source and detector paths 26 and 28, as described previously, and typically includes at least a portion of the β axis. An inner central volume 230 can be defined by surface S2 of housing 78 and can typically enclose scan volume 228. Inner central volume 230 can also be defined by door 176 when closed, as shown in FIG. 14C. Peripheral gap 38 is contiguous with inner central volume 230 when door 176 is in open position (e.g., fully or partially opened).

FIG. 14A shows source transport 32 and detector transport 34 at one extreme end of the scan path, which may be at either the beginning or the end of the scan. FIG. 14B shows source transport 32 and detector transport 34 at the other extreme end of the scan path. It should be noted that source 22 is offset along source transport 32. With this asymmetry, the extent of travel of source 22 relative to surface S3 of housing 78 differs from its extent of travel relative to surface S4. At the extreme travel position shown in FIG. 14B, source 22 is more than twice the distance from surface S4 as source 22 is from surface S3 at the other extreme travel position shown in FIG. 14A. In one embodiment, the inventors use this difference to gain additional clearance for patient positioning with the patient seated.

FIG. 14C shows the configuration of housing 78. In the context of the present disclosure, top surface 190 is considered to be aligned with the top of, at least partially above, or above scan volume 228; bottom surface 192 is aligned with the bottom of, at least partially below, or below scan volume 228. In one embodiment, the top surface 190 or the bottom surface 192 can intersect a portion of the scan volume 228. As shown in FIG. 14C, scan volume 228 can be cylindrical or circularly cylindrical. However, exemplary embodiments of the application are intended to be used with other known 2D scan areas and/or 3D scan volumes. The cover of housing 78 can be metal, fiberglass, plastic, or other suitable material. According to an embodiment, at least portions of top and bottom surfaces 190 and 192 are substantially flat.

As shown in FIGS. 14A-14C, the scanner 110 has a number of surfaces that define its shape and the shape of peripheral gap or opening 38:

-   -   (i) an outer connecting surface S1 extends between a portion of         top surface 190 and a portion of bottom surface 192 to at least         partially encompass the source and detector; at least a portion         of the outer connecting surface extends outside the path the         source travels while scanning; embodiments of the outer         connecting surface S1 shown in FIGS. 14A-14C provide an arcuate         surface that is generally circular at a radius R5 about center β         and that extends, between edges E1 and E2 of the housing;     -   (ii) an inner connecting surface S2 extends between a portion of         the first surface and a portion of the second surface to define         an inner central volume 230 that includes a portion of scan         volume 228; in the embodiment shown in FIG. 14D, inner         connecting surface S2 is approximately at a radius R4 from the β         axis. At least portions of inner connecting surface S2 can be         cylindrical.     -   (iii) other connecting surfaces can optionally include a surface         S3 that corresponds to a first endpoint of the travel path for         source transport 32 (FIGS. 14A-14B) and is adjacent to curved         surface S1 along an edge El, wherein surface S3 extends inward         toward curved inner surface S2; and a surface S4 that         corresponds to a second endpoint at the extreme opposite end of         the travel path from the first endpoint for source transport 32         and is adjacent to curved surface S1 along an edge E2 wherein         surface S4 extends inward toward curved inner surface S2.         According to an embodiment, surfaces S3 and S4 are substantially         flat and the angle between surfaces S3 and S4 is greater than         about 90 degrees. In general, other additional surface segments         (e.g., short linear or curved surface segments) may extend         between or comprise any of surfaces S1-S4.

Inner and outer connecting surfaces S1, S2, and, optionally, other surfaces, define peripheral gap or opening 38 that is contiguous with the inner central volume 230 and extends outward to intersect the outer connecting surface S1 to form gap 38 as an angular recess extending from beyond or toward where the outer connecting surface S1 would, if extended, cross the opening 38. As shown in FIG. 14D, a central angle of a first arc A1 that is defined with a center located within the scan volume and between edges of the peripheral gap 38 determined at a first radial distance R4 outside the scan volume is less than a central angle of a second arc A2 that is defined with the first arc center and between the edges of the peripheral gap 38 at a second radial distance R3 outside the scan volume, where the second radial distance R3 is greater than the first radial distance R4. In one embodiment, as shown in FIG. 14D, a first distance that is defined between edges of the peripheral gap 38 determined at a first radial distance R4 outside the scan volume is less than a second distance between the edges of the peripheral gap 38 at a second radial distance R3 outside the scan volume, where the second radial distance R3 is greater than the first radial distance R4. According to one embodiment, arcs A1 and A2 are centered about the 13 axis, as shown in FIG. 14D and edges of gap 38 are defined, in part, by surfaces S3 and S4 of housing 78.

The needed room for patient anatomy, such as that described with reference to FIG. 10, can be provided when the central angle for arc A2 is large enough to accommodate the extremity that is to be imaged. According to one embodiment, the central angle for arc A2 between edges of gap 38 exceeds the central angle for arc A1 by at least about 5 degrees; more advantageously, the central angle for arc A2 exceeds the central angle for arc A1 by at least about 10 or 15 degrees.

The perspective views of FIGS. 8-11 show various configurations of extremity CBCT imaging apparatus 100 for imaging limbs of a patient. For each of these configurations, the limb or other extremity of the patient must be positioned at the center of scanner 110 and space must be provided for the paired extremity. As described herein, peripheral gap or opening 38 is provided to allow access space for the patient and room for other parts of the patient anatomy. Door 176 is withdrawn into the housing 78 until the patient is positioned; then, door 176 is pivoted into place in order to provide a suitable transport path for the imaging receiver, detector 24, isolated from the patient being imaged.

FIG. 13A shows scanner 110 with door 176 in open position, not obstructing opening 38, that is, keeping opening 38 clear, allowing patient access for extremity placement within opening 38. FIG. 13C is a top view that shows scanner 110 with door 176 in closed position, held by a latch 92. Door 176 thus extends into the opening 38, enclosing a portion of opening 38 for imaging of the patient's extremity. A sensor 82 provides an interlock signal that indicates at least whether door 176 is in closed position or in some other position. Movement of internal scanner 110 components such as C-shaped gantry 36 is prevented unless the door 176 is latched shut. A release 90 unlatches door 176 from its latched position. As shown in FIGS. 13C and 13D, handle 76 can be positioned outside of opening 38, such as along surface 51 as shown, for opening or closing door 176. Placement of handle 76, or other type of door closure device, outside of opening 38 is advantageous for patient comfort when closing or opening door 176. As shown in the exemplary embodiment of FIGS. 13C and 13D, handle 76 is operatively coupled with door 176 so that movement of handle 76 in a prescribed direction, such as along the circumference of scanner 110 housing 78 (e.g., a corresponding direction, or in the clockwise direction shown), causes door 176 corresponding movement (e.g., in the same direction). In one embodiment, clockwise movement of handle 76 causes clockwise movement of door 176, extends door 176 into the opening, and closes door 176; counterclockwise movement of handle 76 causes counterclockwise movement of door 176 and opens door 176, so that it does not obstruct the opening or moves to a position that is clear of the opening.

According to one embodiment, the door 176 is manually pivoted, closed, and opened by the operator. This allows the operator to more carefully support the patient and the extremity that is to be imaged. According to an alternate embodiment, an actuator is provided to close or open the door automatically.

FIG. 15 shows the initial position of gantry 36 at an angle θ0 when door 176 has just been closed. Source 22 and detector 24 are at a rest or default position at angle θ0. Detector path 28 extends into the hollow portion of door 176 as shown.

FIG. 15 shows, from a top view, the relative angular rotation of gantry 36 and how the hollow passage 84 provided by door 176 allows a wide angular range of travel for the orbit of detector 24 around the subject being imaged within the scan volume 228. This sequence shows how door 176 covers or surrounds, but does not obstruct, detector path 28 and shows how detector path 28 passes through the hollow interior of door 176 for imaging when the patient is appropriately positioned and door 176 is pivoted into place and latched. According to an alternate embodiment, another feature of door 176 is a closure portion 188 that can cover a door aperture 88 in housing 78 before, during and following door closing.

The perspective view of FIG. 16, with the cover of housing 78 removed for visibility of internal parts, shows another feature of door 176. A closure portion 188 is provided as a part of door 176 to cover the gap that would otherwise be exposed when the door was closed. This covering keeps out dirt and debris and helps to prevent patient contact with, and visibility of, internal moving parts of scanner 110. According to an alternate embodiment, an edge 94 of closure portion 188 is attached to housing 78 and closure portion 188 folds or bends into place as door 176 pivots toward its closed position.

As shown in FIG. 6A, the source 22 and the detector 24 on the gantry 36 run on a portion of an arcuate non-linear guide rail (e.g., slot). However, the mass of a radiation source can be 5×, 10×, 20× or more relative to the mass of a radiation detector. In exemplary CBCT X-ray imaging systems, the combination of the uneven source 22 and detector 24 masses and/or the position of the masses relative to a scanning volume or a center of rotation (e.g., β axis) can create a large imbalance. For example, the unbalanced CBCT gantry mechanism can suffer backlash when the source “tips over” a high position (or low position) of tilted scan geometry.

Accordingly, a counterweight can be added to a detector to move the center of gravity (COG) of a scanner (e.g., scanner 110 or gantry 36) closer to the scanning volume or center of rotation and/or to reduce the mass imbalance of the source and detector. FIGS. 12C, 16, 17A and 17B show the counterweight 182 added to the detector 24. A counterweight being added to a detector can provide advantages for motion control such as but not limited to (i) a force to drive the counter-balanced gantry in all orientations can be reduced, (ii) inertia can be increased and can be more easily controlled and/or (iii) vibration (e.g., between the source and detector) during motion or scanning of the scan volume can be reduced.

A counterweight can include disadvantages to CBCT X-ray imaging systems and/or methods with the more balanced gantry. Preferably, the source 22 and the detector 24 do not move relative to one another during scanning of the scan volume 228. Accordingly, a very strong structure is needed to withstand the bending forces created and/or applied to a gantry 36 by the counterweight 182 (and/or source 22, detector 24). Further, the structure must be sufficient to move the radiation source and detector (with counterweight) in unison.

FIGS. 17A and 17B are diagrams that show additional features of portions of a gantry for a transport mechanism for use in CBCT X-ray imaging systems. As shown in FIGS. 17A and 17B, the frame 174 of the gantry 36 of the transport mechanism 170 can use a massive integrated structure to withstand the bending forces created and/or applied by the counterweight 182, the detector 24 and/or the source 22. Further, the frame 174 can include first or top portion 174 a, second or lower portion 174 b that extend toward or into the scan volume 228, which can be connected by frame connecting portion 174 c. In one embodiment, the portion 174 a, the portion 174 b, and the portion 174 c, can form an interior pocket 174 d (see FIG. 12A) extending at least partially between the portion 174 a and the portion 174 b. FIG. 17B shows an exterior surface of the frame 174 of the gantry 36. As shown in FIGS. 17A and 17B, the frame 174 can be integrally formed, integrated affixed in sections, rigidly connected or the like.

In one embodiment, a detector can include a grid, which can be integral or removably attached. As shown in FIGS. 17A and 17B, in its position against the detector 24 along the detector path, exemplary grid 242 is constrained for six degrees of freedom (DOF). This is provided by three-point constraint against detector 24, two-point constraint against stop 246, and a single point of constraint against bracket 244.

Certain exemplary embodiments of X-ray imaging systems (e.g., volume radiographic imaging systems, CBCT systems) and/or methods for using the same can provide a detector and a counterweight separately (e.g., scanner or gantry) even though the counterweight and detector can be positioned in or traverse the same relative space. In one embodiment, X-ray imaging systems and/or methods can provide a detector and a counterweight near distal ends of separate support arms (e.g., first and second support arms or a detector weight support unit with a counterweight support unit). In other embodiments, a detector and counterweight can be coupled to a gantry mechanism or transport mechanism (e.g., of a scanner) and configured to move independently from one another.

In certain exemplary embodiments, imaging systems (e.g., CBCT systems) can provide two separate supports individually for a detector and a counterweight. Further, separate supports structures can provide the ability to position the detector relative to the source during scanning with reduced or minimal movement or vibration. In certain exemplary embodiments, a weaker, lighter, smaller, different material and/or more flexible support for the counterweight can reduce the total weight of materials from that used to position and support the detector and the counterweight as a single unit. Further, separate supports can allow positioning of the counterweight proximate the detector path while allowing independent motion with increased vibration of the counterweight during scanning that has reduced impact or minimal impact on the quality of the diagnostic radiographic imaging or imaging data obtained. In addition, providing two separate supports individually for a detector and a counterweight can allow different materials (e.g., with different characteristics such as but not limited to density, strength, rigidity, resistance to bending, cost or the like) to be used for respective support structures for the detector and the counterweight.

FIGS. 18A-18D are diagrams that show an exemplary embodiment of a counterweight support mechanism for use with a gantry for a transport mechanism for use in radiographic imaging systems (e.g., CBCT X-ray imaging systems) and/or methods for using the same. As shown in FIGS. 18A-18D, two separate supports can include a detector weight support arm 310 coupled to support the detector 24 and a counterweight support arm 320 (e.g., separate and individually provided) coupled to support a counterweight 382. In certain exemplary embodiments, the detector weight support arm 310 and the counterweight support arm 320 can be made from different materials or combinations of materials. As shown in FIGS. 18A-18D, the detector weight support arm 310 and the counterweight support arm 320 can be coupled at first ends to a gantry 336 and at second (or distal) ends coupled to the detector 24 and the counterweight 382, respectively. In certain exemplary embodiments, the detector weight support arm 310 and the counterweight support arm 320 are separated by a first clearance gap 350 a. In one embodiment, the detector 24 and the counterweight 382 can be separated by a second clearance gap 350 b. Preferably, the detector weight support arm 310 and the counterweight support arm 320 can extend circumferentially around without impinging the scan volume. In one embodiment, the counterweight support arm 320 can include a curved shape of a C-arm or other curved extensions between its mount to the gantry 336 and the counterweight 382. As shown in FIGS. 18A-18D, the detector weight support arm 310 can be positioned inside (e.g., radially or relative to the scan volume) the counterweight support arm 320. Preferably, the source 22 is also mounted to the gantry 336 (or other portion of a transport mechanism). In one embodiment, one or more sources 22 and the detector 24 can be mounted in the gantry 336 that is part of a transport assembly that can be controllably revolved (e.g., rotatable at least partially about a scan volume or axis β).

In certain exemplary embodiments, the counterweight support arm 320 can have any prescribed 3D shape to attach the counterweight 382 to the scanner without crossing the scan volume 228. For example, the counterweight support arm 320 can include the shape of a C-arm or an arcuate extension between a source mount at the gantry and the counterweight. Alternatively, a counterweight support arm can include a curved or non-linear shape between a mount connection to the gantry mechanism and a mount connection to the counterweight. In other embodiments, the counterweight support arm can include a series of linear sections that together form a prescribed form between the gantry mechanism and the counterweight. Any configuration (e.g., mechanical or electro-mechanical) is envisioned that locates the counterweight in the intended position physically separated from the detector, which is mounted to receive radiation from the source across an opening or scan volume. In one embodiment, the detector weight support mechanism and the counterweight support mechanism have similar (or identical) shapes. In one embodiment, a detector weight support mechanism and a counterweight support mechanism have similar sickle shapes. In one embodiment, the detector weight support mechanism or the counterweight support mechanism can include a form that crosses below or above the scan volume. In one embodiment, the detector weight support mechanism or the counterweight support mechanism can have similar shapes that encircle the scan volume.

In certain exemplary embodiments, the detector weight support arm 310 is configured to limit the detector 24 motion during scanning of the scan volume 228 to less than ½, ⅕ or 1/10 of the motion of the counterweight 382 allowed by the counterweight support arm 320 during scanning of the scan volume 228. In one embodiment, the detector weight support arm 310 can connect the detector 24 to the source 22 (e.g., gantry 336) such that less than 5 mm, less than 3 mm or less than 1 mm of motion is created at the detector 24 (e.g., or relative motion between the source 22 and the detector 24) during scanning of the scan volume 228. In one embodiment, the counterweight support arm 320 connects the counterweight 382 to the source 22 (e.g., gantry 336) such that less than 12 mm, less than 8, or less than 3 mm of motion is created at the counterweight 382 during scanning of the scan volume 228. In one embodiment, the detector weight support arm 310 can secure the detector 24 to a gantry mechanism with reduced movement as compared to known configurations where the detector and counterweight move and/or are mounted as a single unit (e.g., using frame 174).

In certain exemplary embodiments, providing two separate supports individually for a detector and a counterweight can provide the ability to provide a prescribed size clearance gap between the detector and the counterweight. In one embodiment, the clearance gap can be a preset 3-dimensional gap, a 2-dimensional gap or a distance between the detector weight support arm 310 and the counterweight support arm 320 (or between the detector 24 and the counterweight 382). In one embodiment, a clearance gap can be set responsive to (e.g., proportional, weighted, non-linear) to the amount of calculated movement (e.g., deflection) and/or actual movement of the counterweight 382 during scanning of the scan volume 228 or during any movement of a CBCT radiographic imaging system. In one embodiment, a clearance gap can be set responsive to (e.g., proportional, weighted, non-linear) to the amount of calculated movement (e.g., deflection) and/or actual movement of the detector 24 (source movement, relative movement between detector and source, scanner, etc.) during scanning of the scan volume 228 or during any movement of the CBCT radiographic imaging system.

In certain exemplary embodiments, providing two separate supports individually for the detector and the counterweight can provide increased bore size and/or increased scan volume of a CBCT radiographic imaging system. In certain exemplary embodiments, providing two separate supports individually for the detector 24 and the counterweight 382 can provide the ability to increase a bore size and/or increase a scan volume of a CBCT radiographic imaging system. Preferably, while maintaining or reducing calculated or actual movement between the source 22 the detector 24 during scanning of the scan volume 228.

FIGS. 19A-19B are diagrams that show an exemplary embodiment of a counterweight support mechanism for use with a gantry for a transport mechanism for use in CBCT radiographic imaging systems or the like. As shown in FIGS. 19A-19B, two separate supports can include a detector weight support arm 410 coupled to support the detector 24 and counterweight support arm 420 (e.g., separate and individually provided) coupled to support a counterweight 482. As shown in FIGS. 19A-19B, the detector weight support arm 410 and the counterweight support arm 420 can be coupled at first ends to a gantry and at second (or distal) ends coupled to the detector 24 and the counterweight 482, respectively. In certain exemplary embodiments, the detector weight support arm 410 and the counterweight support arm 420 are separated by a first clearance gap 450 a. In one embodiment, the detector 24 and the counterweight 482 can be separated by a second clearance gap 450 b. Preferably, the detector weight support arm 410 and the counterweight support arm 420 can extend outside or circumferentially around without impinging the scan volume. As shown in FIGS. 19A-19B, the detector weight support arm 410 can be positioned inside (e.g., radially or relative to the scan volume) the counterweight support arm 420 so that a paired extremity can pass therebetween. Preferably, the source 22 is also mounted to the gantry 336.

FIGS. 20A-20B are diagrams that show an exemplary embodiment of a counterweight support mechanism for use with a gantry for a transport mechanism for use in CBCT radiographic imaging systems or the like. As shown in FIGS. 20A-20B, two separate supports can include a detector weight support arm coupled to support the detector 24 and counterweight support arm (e.g., separate and with multiple extensions) coupled to support a counterweight 482. As shown in FIGS. 20A-20B, a detector weight support arm 510 and/or the counterweight support arm can be formed as a plurality of support arms/units (e.g., mechanically or electro-mechanically connected or separated) coupled at one or more first ends to a gantry and at one or more second (or distal) ends coupled to the detector 24 and the counterweight 482, respectively.

In certain embodiments, a detector weight support arm and/or a counterweight support arm are shown as separate units that are attached to the gantry 36 (or scanner 110). In alternative exemplary embodiments, detector weight support arm and/or a counterweight support arm can be integrally formed as a single unit with one or more portions of a transport mechanism (e.g., gantry 36) or a scanner 110.

Radiographic imaging systems typically use a linear grid as an anti-scatter device that improves contrast and signal to noise (S/N) ratio in radiographic images. A grid typically includes a series of lead foil strips that block x-rays separated by spacers that are transmissive to x-rays. The spacing of the strips determines the grid frequency, and the height-to-distance between lead strips determines a grid ratio. These and other grid characteristics can vary depending on the radiation energy that is used for a particular image. Calibration of the detector takes grid characteristics into account, so that different calibration data are used for different grids. In certain exemplary embodiments herein, a detector can include a grid, which can be integral or removably attached to the detector. Certain exemplary embodiments according to the application can provide grid access (e.g., through door 176) for replacement with a different grid or removal of the grid from the imaging path. In one embodiment, a detector does not include a grid.

Consistent with at least one embodiment, exemplary methods/apparatus can use a computer program with stored instructions that perform on image data that is accessed from an electronic memory. As can be appreciated by those skilled in the image processing arts, a computer program of an embodiment herein can be utilized by a suitable, general-purpose computer system, such as a personal computer or workstation. However, many other types of computer systems can be used to execute the computer program of described exemplary embodiments, including an arrangement of networked processors, for example.

The computer program for performing methods of certain exemplary embodiments described herein may be stored in a computer readable storage medium. This medium may comprise, for example; magnetic storage media such as a magnetic disk such as a hard drive or removable device or magnetic tape; optical storage media such as an optical disc, optical tape, or machine readable optical encoding; solid state electronic storage devices such as random access memory (RAM), or read only memory (ROM); or any other physical device or medium employed to store a computer program. Computer programs for performing exemplary methods of described embodiments may also be stored on computer readable storage medium that is connected to the image processor by way of the internet or other network or communication medium. Those skilled in the art will further readily recognize that the equivalent of such a computer program product may also be constructed in hardware.

It should be noted that the term “memory”, equivalent to “computer-accessible memory” in the context of the present disclosure, can refer to any type of temporary or more enduring data storage workspace used for storing and operating upon image data and accessible to a computer system, including a database, for example. The memory could be non-volatile, using, for example, a long-term storage medium such as magnetic or optical storage. Alternately, the memory could be of a more volatile nature, using an electronic circuit, such as random-access memory (RAM) that is used as a temporary buffer or workspace by a microprocessor or other control logic processor device. Display data, for example, is typically stored in a temporary storage buffer that can be directly associated with a display device and is periodically refreshed as needed in order to provide displayed data. This temporary storage buffer can also be considered to be a memory, as the term is used in the present disclosure. Memory is also used as the data workspace for executing and storing intermediate and final results of calculations and other processing. Computer-accessible memory can be volatile, non-volatile, or a hybrid combination of volatile and non-volatile types.

It will be understood that computer program products for exemplary embodiments herein may make use of various image manipulation algorithms and processes that are well known. It will be further understood that exemplary computer program product embodiments herein may embody algorithms and processes not specifically shown or described herein that are useful for implementation. Such algorithms and processes may include conventional utilities that are within the ordinary skill of the image processing arts. Additional aspects of such algorithms and systems, and hardware and/or software for producing and otherwise processing the images or co-operating with the computer program product of the application, are not specifically shown or described herein and may be selected from such algorithms, systems, hardware, components and elements known in the art.

It should be noted that while the present description and examples are primarily directed to radiographic medical imaging of a human or other subject, embodiments of apparatus and methods of the present application can also be applied to other radiographic imaging applications. This includes applications such as non-destructive testing (NDT), for which radiographic images may be obtained and provided with different processing treatments in order to accentuate different features of the imaged subject.

Although sometimes described herein with respect to CBCT digital radiography systems, embodiments of the application are not intended to be so limited. For example, other DR imaging system such as dental DR imaging systems, mobile DR imaging systems or room-based DR imaging systems can utilize method and apparatus embodiments according to the application. As described herein, an exemplary flat panel DR detector/imager is capable of both single shot (radiographic) and continuous (fluoroscopic) image acquisition. Further, a fan beam CT DR imaging system can be used.

Exemplary DR detectors can be classified into the “direct conversion type” one for directly converting the radiation to an electronic signal and the “indirect conversion type” one for converting the radiation to fluorescence to convert the fluorescence to an electronic signal. An indirect conversion type radiographic detector generally includes a scintillator for receiving the radiation to generate fluorescence with the strength in accordance with the amount of the radiation.

Exemplary embodiments according to the application can include various features described herein (individually or in combination). Priority is claimed from commonly assigned, copending U.S. provisional patent application Ser. No. 61/710,832, filed Oct. 8, 2012, entitled “Extremity Scanner and Methods For Using The Same”, in the name of John Yorkston et al., the disclosure of which is incorporated by reference.

While the invention has been illustrated with respect to one or more implementations, alterations and/or modifications can be made to the illustrated examples without departing from the spirit and scope of the appended claims. In addition, while a particular feature of the invention can have been disclosed with respect to one of several implementations, such feature can be combined with one or more other features of the other implementations as can be desired and advantageous for any given or particular function. The term “at least one of” is used to mean one or more of the listed items can be selected. The term “about” indicates that the value listed can be somewhat altered, as long as the alteration does not result in nonconformance of the process or structure to the illustrated embodiment. Finally, “exemplary” indicates the description is used as an example, rather than implying that it is an ideal. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. 

The invention claimed is:
 1. A method for cone beam computed tomography, the method comprising the steps of: moving a detector about an imaging axis along at least a portion of a circular detector path using a C-shaped gantry to support the detector; moving a source about the imaging axis along at least a portion of a circular source path, using the C-shaped gantry, simultaneously with the step of moving the detector, the source disposed to face the detector directly across the imaging axis during the movement of the source and the detector about the imaging axis; attaching a counterweight to the C-shaped gantry adjacent the detector so that the counterweight moves simultaneously with the movement of the source and the detector about the imaging axis attaching a C-shaped detector weight support arm to the detector and to the C-shaped gantry, the C-shaped detector weight support arm configured to support and to move the detector, and attaching a C-shaped counterweight support arm to the gantry and to the counterweight, the C-shaped counterweight support arm configured to support and to move the counterweight.
 2. An imaging apparatus for cone beam computed tomography imaging, the apparatus comprising: at least one support column; and a scanner coupled to the at least one support column, the scanner comprising: a C-shaped gantry; a radiation source coupled to a proximal end of the C-shaped gantry; a radiation detector coupled to a distal end of the C-shaped gantry; a counterweight attached to the distal end of the C-shaped gantry adjacent to the radiation detector; and a C-shaped housing enclosing the C-shaped gantry, the radiation source, the radiation detector and the counterweight, wherein the C-shaped gantry is configured to revolve both the radiation detector and the radiation source simultaneously about an imaging axis during a scanning procedure to acquire radiographic image data in the radiation detector according to radiation received from the radiation source, an imaging surface of the radiation detector faces the radiation source along a line that intersects the imaging axis, and wherein the scanner is configured to move in at least three dimensions including a vertical movement along a track in the at least one support column, a rotational movement about a first axis perpendicular to the imaging axis, and a rotational movement about a second axis perpendicular to the imaging axis and the first axis, and wherein the scanner further comprises: a C-shaped detector weight support arm, a proximal end of the C-shaped detector weight support arm coupled to the proximal end of the C-shaped gantry, and a distal end of the C-shaped detector weight support arm coupled to the radiation detector; and a C-shaped counterweight support arm, a proximal end of the C-shaped counterweight support arm coupled to the proximal end of the C-shaped gantry, and a distal end of the C-shaped counterweight support arm coupled to the counterweight in a position adjacent to the radiation detector.
 3. The imaging apparatus of claim 2, wherein the C-shaped counterweight support arm is configured to provide independent movement of the counterweight relative to the detector.
 4. The imaging apparatus of claim 2, wherein the C-shaped counterweight support arm is configured to provide a prescribed size clearance gap between the detector and the counterweight.
 5. The imaging apparatus of claim 2, wherein relative motion of the counterweight during the scanning procedure is at least 5× greater than the motion of the detector during the scanning procedure.
 6. The imaging apparatus of claim 2, wherein the C-shaped detector weight support arm and the C-shaped counterweight support arm are parallel to one another, and wherein one of the C-shaped detector weight support arm and the C-shaped counterweight support arm is closer to the imaging axis.
 7. The imaging apparatus of claim 2, wherein the C-shaped detector weight support arm and the C-shaped counterweight support arm are made from different materials.
 8. The imaging apparatus of claim 2, wherein the counterweight is configured to reduce vibration of the imaging apparatus during the scanning procedure.
 9. The imaging apparatus of claim 2, wherein the C-shaped detector weight support arm is configured such that less than 10 mm of motion is created at the detector relative to the source during the scanning procedure.
 10. The imaging apparatus of claim 2, wherein the C-shaped detector weight support arm is configured to limit detector motion during the scanning procedure to less than 1/10 of the motion of the counterweight during the scanning procedure.
 11. The imaging apparatus of claim 2, wherein the C-shaped housing is configured to provide a gap in the detector path and the source path for radial access to the imaging axis, and wherein the scanner further comprises a door that moves into the gap from a first position that does not obstruct the gap to a second position that extends into the gap.
 12. The imaging apparatus of claim 4, wherein the detector on the C-shaped detector weight support arm and the counterweight on the C-shaped counterweight support arm are separately provided with a gap therebetween, and wherein the prescribed size clearance gap is responsive to a movement amount of the counterweight. 